<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <ul>
      <li>1</li>
      <li>2</li>
      <li>3</li>
      <li>4</li>
    </ul>

    <script>
      //方式一
      //   var lis = document.getElementsByTagName("li");
      //   lis[0].innerHTML = "修改了";
      //   lis[1].innerHTML = "修改了";
      //   lis[2].innerHTML = "修改了";

      //方式二
      var lis = document.getElementsByTagName("li");
      for (var i = 0; i < lis.length; i++) {
        lis[i].innerHTML = "修改了";
      }

      var obj = {
        age: 20,
      };
      var myage = "age";
      console.log(obj.myage); //会把myage当成字符串
      console.log(obj[myage]); //会把myage当成变量解析; -->obj["age"]
    </script>
  </body>
</html>
